Kidney stone disease is a substantial health problem associated with significant pain, suffering, and economic costs. 5% to 15% of the population will have a symptomatic episode of a stone within the urinary tract by the age of 70 and at least 50% of these individuals will have recurrent stone disease. This grant focuses on the attachment of urinary crystals to injured kidney papillary tip epithelium. Our investigations are driven by the working hypothesis that crystal attachment to papillary epithelium requires cell/tissue injury that includes loss of cell plasma lipid asymmetry and/or loss of cell polarity. Two specific inner medullary collecting duct (IMCD) cell injury models will be employed. (i) the loss of plasma membrane lipid asymmetry resulting in the presentation of phosphatidylserine from the inner to the outer leaflet of the cell plasma membrane, and (ii) the loss of cell polarity as a result of intracellular tight junction breakdown resulting in the mixing of plasma membrane basolateral and apical membrane components to an altered luminal cell surface. In both models, injury leads to altered apical membrane composition/structure, and more importantly converts a non-crystal attaching cell into one that does attach crystals. The proposed studies are divided into three Specific Aims that test three specific hypotheses. They will utilize established cell culture and isolated perfused tubule systems and a hyperoxaluric animal model of stone disease. Investigations will be limited to the four most common crystalline components of human urinary tract stones, namely calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD), basic calcium phosphate (apatite, AP), and uric acid (UA) crystals. The Specific Aims are: Specific Aim I: To determine in injured papillary collecting duct cells the influence of urinary environment on the molecular nature of crystal attachment in molecules on the altered plasma membrane surface. Specific Aim II: To determine the relative susceptibility of two specific nephron segments to defined injury and subsequent attachment of crystals. Specific Aim III: To determine in an animal model if mild chronic hyperoxaluria produces the localized nephron cell injury that precedes crystal attachment during supersaturation conditions and episodes of crystalluria.